Make background volume commits default experience

[thundergolfer]

Describe your changes

Previously if a user didn't specify the flag they wouldn't get background commits. When this merges they will.

#1823 merged only a few days ago. I'll merge this around mid-week next week.

cc @gimaker

Backward/forward compatibility checks

• Client+Server: this change is compatible with old servers
• Client forward compatibility: this change ensures client can accept data intended for later versions of itself

Changelog

• Background committing on modal.Volume mounts is now default behavior.

[modal-pr-review-automation]

Auto-approved 👍. This diff qualified for automatic approval and doesn't need follow up review.

[gimaker]

👍